A conventional emergency core cooling system for a pressurized-water reactor ordinarily comprises a single accumulator containing a supply of emergency core cooling water, and connected to a single check valve so as to feed in parallel into the hot and cold legs of the reactor's coolant loop. The accumulator pressure is less than the pressure of the reactor coolant under normal operating conditions. In the event of a loss-of-coolant accident, the reactor coolant pressure drops to below the accumulator pressure, the check valve, previously held closed by the reactor coolant pressure, then opening under the accumulator pressure, the emergency core cooling water then being injected as parallel flows, simultaneously into both legs of the coolant loop.
The reactor has its core contained within a pressure vessel having connections with the hot and cold legs of the coolant loop, and internally constructed to form a lower or cold plenum into which the reactor coolant flows from the cold leg, for upward travel through the core, and an upper or hot plenum which receives the coolant, now heated by its core cooling action, and which connects with the hot leg. Ordinarily the emergency core cooling water is simultaneously injected into both plenums by connections with these legs of the coolant loop.
The coolant loop comprises the pressure vessel, the pipe forming the hot leg and which connects with a heat exchanger (a steam generator for producing power), and the pipe line forming the cold leg and which through the main coolant pump carries the coolant back to the pressure vessel. Any break in this loop permits the pressurized-water coolant to escape and stops the coolant circulation through the reactor core which then rapidly overheats. The accident drops the pressure in the two plenums and results in the injection of the emergency core cooling water into these plenums with the object of flooding the core as quickly as possible until other portions of the system can start a circulation of water into the core. The emergency core cooling system involves other functions which need not be described in connection with the present subject matter.
The simultaneous injection of the emergency water into both plenums has been considered to be important to provide the redundancy of safety precautions required in the case of nuclear installations.
However, the cooling efficiency and speed thus obtained, should be improved if possible, and such improvements is the object of the present invention.